What is best way to go after a tenant for rental debt?

[David To]

I have a tenant that owes me about $30K in rental debt in San Diego. I will pursue through small claims court after March, 2021. The problem is this.

1) when tenant moves out, they don't have to provide me a forwarding address

2) they could also change their email and or cell phone number as well

3) my attorney says it's a conflict of interest to try and get the tenant's forwarding address from the tenant's attorney (they will most likely not provide this information)

4) I do have the tenant's driver's license and US passport

So how do I go about obtaining the tenant's present address when there's no obligation on their part to provide it. Since small claims court requires you to know their present address in order to serve them.

So just wondering how previous landlords have gone about this. 

1) do you hire a private investigator? If so, please provide some contacts in Southern California (Los Angeles, San Diego) for me.

2) do you hire a profession collection agency? If so, please provide some contacts in Southern California (Los Angeles, San Diego) for me.

3) also, what database or website do landlords use to place this tenant on the list of tenants that landlords should avoid at all cost? I would like to include this tenant on the list as well.

Thanks for reading and hopefully some people will reply with good insight to this.